1. Field of the Invention
The present invention relates to a head rest apparatus provided in a seat back in a seat for automobiles and reducing a whiplash syndrome applied to a passenger at a time of being collided from rear-end or the like.
2. Background Art
FIG. 4 shows an inner structure of a reclining type seat back provided with a conventional head rest apparatus 30. In FIG. 4, reference numeral 21 denotes a seat back frame formed in a substantially reverse-U shape as seen from a front face. The seat back frame 21 is mounted to a seat cushion (not shown) via a reclining shaft 22 provided in a lower end so as to freely tilt. The head rest apparatus 30 is provided in upper end portions of right and left vertically extending portions of the seat back frame 21 via brackets 23.
The apparatus 30 is mainly constituted by a C-shaped head rest frame 31 mounted to each of the brackets 23 via a tilting shaft so as to freely tilt in a longitudinal direction, a pressure receiving plate 32 fixed to a lower end portion of the head rest frame 31, and coil springs 33 always urging the head rest frame 31 in a backward tilting direction. Head rest holders 34 to which stays of a head rest (not shown) are attached are mounted to upper end portions of the head rest frame 31. The coil springs 33 are provided between the seat back frame 21 and end portions of the pressure receiving plate 32, and pull the pressure receiving plate 32 forward, thereby always urging the head rest frame 31 in a backward tilting direction. With respect to an attaching aspect of the coil springs 33, as shown in FIG. 6, there is a case of being connected to the pressure receiving plate 32 from the seat back frame 21 via links 35. The head rest holders 34 are brought into contact with the upper end portion of the seat back frame 21, whereby the head rest frame 31 is restricted from being backward tilted more over, and is held at a fixed position.
In accordance with the head rest apparatus 30 mentioned above, when a passenger sitting on the seat relatively moves backward due to a reaction of a shocking forward acceleration of an automobide caused by a rear-end collision or the like, the pressure receiving plate 32 is backward pressed against the urging force of the coil springs 33. Following to this motion, the head rest frame 31 tilts forward around the tilting shaft corresponding to a supporting point, and the head rest moves forward so as to support a head portion of the passenger. FIG. 7 shows a state in which a human body M of the passenger moves backward and the head rest 36 moves forward. As mentioned above, the head rest positively moves forward so as to support the head portion of the passenger, whereby a whiplash syndrome applied to the passenger is reduced.
In the conventional head rest apparatus 30 mentioned above, the coil springs 33 urging the head rest frame 31 in the backward tilting direction has a layout for pulling the pressure receiving plate 32 from the forward. Accordingly, as shown in FIG. 8, the human body M of the passenger pressing the cushion 24 of the seat back and moving backward is easily interfered with the coil springs 33, and there is a case that the coil springs 33 are interfered with the seat back frame 31, so that there is a risk that the head rest apparatus 30 does not reliably operate. Further, since it is impossible to secure a sufficient distance (denoted by reference symbol L) from the coil spring 33 to the surface of the cushion 24, it is necessary to form a pad member such as an urethane foam or the like constituting the cushion 24 thin, however, this formation requires a difficulty. Further, there is a requirement of reducing a thickness and a width of the seat back according to some sizes of the automobile and some layouts of the seat, and in this case, it is difficult to provide with the head rest apparatus 30 using the coil springs 33 mentioned above in the seat.